Project Description
In 2024, Foundex was retained to drill jet‑grout verification PQ core holes from inside one of the shafts of the Annacis Water Supply Tunnel prior to the tunnel boring machine daylighting into the shaft.
Foundex modified the HT‑500 rotary drill, tooling, and support equipment to enable it to be lowered into the bottom of the shaft by a tower crane to a depth of approximately 60 metres below ground surface. To drill through the grout columns, core holes were inclined at a shallow upward angle (15° from horizontal). Each exploratory hole was outfitted with a section of PWT casing, set and cemented in place at each hole collar. In the event that the jet‑grout column was not successful in sealing the formation around the shaft, and to mitigate the risk of groundwater inflow to the shaft through the core hole, a custom inflatable annular diverter was installed on the casing cemented into the side of the shaft. This diverter and shut‑in assembly permitted safe closure of the hole if excessive water ingress was encountered.
After each hole was cored to target depth, the hole was left open for three days to allow monitoring for potential groundwater inflow through the core hole. While monitoring was ongoing, the shut‑in diverters remained installed on the casing, and the drill rig was repositioned to the next location to begin drilling.
Once the monitoring period was complete, a cement grout mixture was used to abandon and seal each of the core holes.
